1. Field of the Invention
The present invention relates generally to power amplifiers used for transmitting RF energy and, in particular, to a multi-stage amplifier wherein the stages are arranged in parallel and switchably turned on or off to provide a desired plurality of power levels with each stage operating at a predetermined operating point.
2. Description of Related Art
A power amplifier of one type or another is used as the final stage in any RF transmission device. In a cellular telephone, for example, the power amplifier receives a signal as an input and then amplifies that signal to a power level that may be effectively coupled to an antenna and transmitted as RF radiation. Currently, most power amplifiers utilize multiple amplifier stages connected in series to form a multi-stage power amplifier. In the modem transceiver the transmitted power is adjusted by varying the series connected power amplifier""s bias voltage or current.
However, by adjusting the bias voltage or current in a series connected multi-stage amplifier for a plurality of power levels, the efficiency is known to be 60% or less resulting in wasted power to heat. Therefore, there is a need for a multi-stage power amplifier that is capable of operating at a plurality of power levels at a higher overall average efficiency. The subject invention solves this problem in a new and unique manner not previously known in the arts.
The method and system comprises a multi-stage power amplifier having a plurality of power amplifier stages arranged in parallel with associated switches for selectively switching the plurality of power amplifier stages on or off to produce a desired power level.
Selectively switching on or off each individual power amplifier""s associated switches at predetermined operating point""s produces the desired power level for maximum efficiency. Additionally, more than one connected multi-stage power amplifier, each having a plurality of power amplifier stages, arranged in parallel with associated switches for selectively switching on or off the plurality of power amplifier stages may be used to produce a desired power level.